Coating compositions typically include a primary binder resin, a cross-linking agent, a pigment or pigments to improve the aesthetics of the coating composition, and other coating additives such as solvents, flow and appearance control agents, fillers such as extender pigment, and the like.
It is understood in the art that the pigment is incorporated into the coating compositions via a pigment dispersion. The pigment dispersion is derived from dispersion of the pigment into a pigment dispersant. More specifically, a mill, such as a ball mill, grind mill, or continuous mill, is utilized to incorporate the pigment into the pigment dispersant. The mill integrates the pigment into the pigment dispersant until a desired particle size of the pigment is achieved, and until the pigment is appropriately wetted by the pigment dispersant and uniformly dispersed throughout the pigment dispersant.
The pigment dispersants of the prior art including, but not limited to, polyacrylate-based emulsions, have proven to be inadequate for use as a pigment dispersant for dispersing pigment usable in coating compositions. The pigment dispersants of the prior art are ineffective because these resins are unable to withstand mechanical forces exerted by the mill when integrating the pigment. These pigment dispersants are also deficient in wetting the pigment and in maintaining the pigment dispersed throughout the pigment dispersant. Instead, with the pigment dispersants of the prior art, such as the polyacrylate-based emulsion pigment dispersant, the pigment tends to coagulate or settle resulting in poor stability and inadequate ‘shelf life’ of the pigment dispersion. One aspect of poor stability results from having a pH which is too basic. The pigment dispersants having high pH values tend to show increased coagulation and decreased ‘shelf life’ of the pigment dispersion.
These prior art pigment dispersants also tend to have increased viscosities and, as understood in the art, increased viscosities typically inhibit the amount of pigment that can be incorporated into the pigment dispersant. As a result, pigment dispersions that utilize the pigment dispersants of the prior art cannot attain sufficient pigment-to-binder ratios while maintaining acceptable gloss and appearance in a film of the coating compositions. Also, due to the increased viscosity, these pigment dispersants often require solvent and other additives which increases the overall volatile content of the pigment dispersion—a characteristic that is undesirable throughout the coating industry.
In sum, the prior art pigment dispersants, as detailed above, are characterized by one or more inadequacy. Due to the inadequacies identified in the prior art, it is desirable to provide a polymeric pigment dispersant to be utilized as a grind resin for inorganic pigments and a method of preparing the polymeric pigment dispersant. It is advantageous that the polymeric pigment dispersant according to the subject invention has improved stability, effectively wets pigment, uniformly disperses pigment, provides increased pigment-to-binder ratios, and increases pigment loading accompanied with acceptable gloss and appearance in the film of the coating composition.